In the usual pneumatic power system of a vehicle, such as a truck having air actuated brakes and other devices, a pneumatic compressor is driven by belts extending from the truck engine and has a selectively engageable clutch actuated by a pressure sensing switch. When the power demand is high, such as during braking operations, the compressor runs and provides pressurized air to a reservoir or holding tank. When the pressure in the tank falls below a certain limit, such as 120 pounds, the pressure sensitive switch causes the clutch to engage and the compressor to start operation.
Normally, the air intake line for the compressor is connected to the engine air induction manifold through which air is drawn into the engine cylinders during downstrokes of the pistons. A substantial vacuum or negative pressure is created in the induction manifold and during operation of the compressor, air is further drawn from the manifold. The air first travels through a filter for cleaning and is then normally compressed in some manner, such as by turbo charging or supercharging prior to entering the induction manifold.
As long as the compressor is also drawing or pulling air through the induction manifold, operation of the pneumatic power system remains satisfactory; however, when the compressor shuts off for any reason, such as sufficient tank pressure, the drawing power of the engine pistons tend to pull a vacuum or create a negative pressure in the compressor inlet conduit. This negative pressure also reaches the internal compression means of the compressor, such as a rotor or pistons, and tends to create a negative pressure in the compression chambers, pulling oil upwardly from the compressor oil sump wherein the oil tends to accumulate in the chambers. When the compressor again commences operation, the mixture of oil and pressurized air tends to be pushed into the reservoir or tank and from there into the air actuated devices, such as the brakes. This contamination can be very dangerous and in many cases can lead to brake failure with resultant injuries to life and property.
The present invention provides a check valve in the intake line to break or interrupt the accumulation of vacuum pressure in the line from reaching the compressor, thereby preventing the vacuum drawing of oil into the compressor chambers. The valve is readily installed in existing pneumatic power systems and is sufficiently inexpensive to make such a retrofit economical.